The present invention is directed to the field of wheelchairs and other medical devices. In particular, the present invention is directed to a brake to allow the user to safely exit from the wheelchair or walker. One problem with the existing devices is that when the user stands up or tries to exit or enter the wheelchair or other medical device, there is the possibility that the wheelchair or walker will start to roll backwards. When that happens, the user may not be entirely out and may fall backwards as the device rolls in that direction. The available devices may include manual brakes on the wheels in an attempt to prevent such falling. However, often times a caregiver may forget to set the brake and the patient may fall if he or she attempts to exit or enter on his or her own. The object of the present invention is to solve this problem by providing an automatically engaging safety device.